How Do Self-Drilling Hollow Rock Bolts Support Backfill Foundation Slopes?

by Anna S. Optimization Specialist

The common support methods for backfill foundation pit slopes include ordinary rock bolt support and casing drilling support. These construction processes may cause problems such as slow and difficulty in drilling, holes collapsing, blockage of grouting channels, difficulty in ensuring grouting effect, and material waste, which may affect the construction progress. To ensure the project can be completed smoothly, Sinorock recommends using self-drilling hollow rock bolts.

Difficulties in Backfill Foundation Slope Support

Collapsed Hole

The backfill soil is loose and the composition is relatively complex. Reliable wall protection measures should be taken to the foundation slope support, otherwise, the problem of hole collapsing will easily occur. However, if the casing wall construction encounters large debris, it will also face the problem of difficult hole formation.

Localized Deformation

The backfill soil has large porosity, high water content, and a lot of organic matter and humic substances, which leads to a decrease in the bearing capacity of the foundation, a large deformation, and low shear strength. The phenomenon of localized deformation reduction may occur in the support material under tensile stress.

Poor Grouting Effect

The trickiest point of reinforcing the backfill foundation slope with rock bolts is that the soil cannot provide enough cohesion, and the rock bolts are likely to fail to reach the designing ultimate load. Since the miscellaneous fill contains hard objects such as bricks and slag, ordinary soil nails cannot form holes. If the construction of the anchor rod adopts the follow-pipe drilling process, it is difficult to ensure that the anchor rod can reach the design load by grouting.

Self-Drilling Hollow Rock Bolt Support Technology

Locate Drilling Positions

Determine the location of each drill hole according to the design drawings. When drilling, the construction shall be carried out according to the design angle.

Connect the Anchor Rod and Drill Bit

It is necessary to select the material and structure of the drill bit according to different geology. The rod body of the self-drilling hollow grouting anchor rod is the drill rod and the grouting pipe. The drilling can be realized by connecting the anchor rod and the drill bit with the grouting hole. The function of grouting and anchoring is integrated.

Synchronous Drilling and Grouting

The rod body of the self-drilling bolt can be used as a grouting pipe. The grouting material is pure cement slurry, which is stirred evenly. The grouting pressure needs to be ≥1.5MPa. If necessary, secondary grouting or grouting is required to ensure the pull-out force value of the bolt.

Lengthen the Anchor Rod

Choose whether to match the connecting sleeve according to the drilling depth. After the anchor rod is drilled in place, install the connecting sleeve at the end of the anchor rod, and then install the second-rod body on the other end of the connecting sleeve and continue drilling.

Pull Test

After the cement slurry solidifies, it will be combined with the anchor rod and the surrounding rock mass to form a section of the anchor body, and the mutual friction between the three will generate a pull-out force. It needs to be tested to prove that the pull-out bearing capacity meets the design requirements.

Self-drilling hollow rock bolts can play the function of "multi-purpose" in backfill foundation pit slope support. They can be used as drill pipes, grouting pipes, and bolt bodies to overcome the problems of collapsed holes and stuck drills. It has the advantages of fast drilling speed and a good grouting effect.

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Created on Aug 12th 2022 04:08. Viewed 160 times.

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